External thermostat fan controller

ABSTRACT

A programmable controller circuit that can be connected directly to the fan switch of any thermostat with a forced air heating and/or cooling system that includes a blower fan for circulating air throughout the home. The controller can be installed with minimal modifications to the existing wiring. The present invention increases the efficiency of the cooling system by evaporating condensate and extracting residual coolness from the thermal mass of the evaporator coils. The present invention can be programmed with a single button. A method of adapting additional fan run time based on compressor run time an AC compressor off time and an AC compressor on time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 61/324,229 filed 2010 Apr. 14 by the present inventor.

FEDERALLY SPONSORED RESEARCH

Not applicable.

SEQUENCE LISTING OR PROGRAM

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is a device for extending the run time of an airconditioning fan after the compressor stops and thereby increasing thecooling/heating output and in the case of air conditioning, increasingthe Sensible Energy Efficiency Ratio (SEER).

2. Description of the Related Art

U.S. Pat. No. 5,142,880 (Bellis, 1992) discloses a solid state controlcircuit for use in connection with existing low-voltage thermostatterminals of a central, forced-air, air conditioning system having acompressor and an indoor blower and gas-fired or electrical heatingelements. The '880 patent relates generally to systems for increasingthe efficiency of air conditioning units by continuing the blowerrunning time after the compressor is turned off. Specifically, the '880patent claims an air conditioning control unit comprising a low voltageroom thermostat fan terminal, a low voltage compressor relay terminal, atiming circuit means, a sensitive gate triac, and a power triac. The'880 patent also claims a method for controlling the on-off time of anindoor fan that is controlled by and associated with an indoorthermostat for a room air conditioning system. The apparatus of the '880patent is not programmable or adaptable. It does not have a fixed delayfrom one system to another. The delay is related to the supply voltage,which varies from system to system. Bellis provides constant current tothe triac gates on the order of 6 milliamps. The total current draw iseven higher than that when all components are included. Many systemshave do not accommodate this much current draw through control relayswithout causing a humming noise which irritates the user. The Bellisdesign momentarily de-energizes the relay when switch from thermostatdriven fan to his delay. This can cause relay chatter and excessivewear. Bellis does not provide for an override function if the unitfails. The Bellis design is a “fixed” delay. The delay does vary withrespect to supply voltage, component variation and temperature. Bellisoutlines between 3 and 5 minutes for the delay. His device is notprogrammable or adaptable.

In U.S. Pat. No. 5,882,233 Noto teaches of a device used to extend thefan run time and also periodically activate the fan during times thesystem is not calling for heating or cooling. Noto requires the circuitto have access to the 24 VAC signals from the AC transformer. Thisrequirement precludes his device from being connected directly to thethermostat since most thermostats do not have both the hot and neutrallegs of the transformer. Household wiring only provides the hot (red)signal to the transformer. Although Noto teaches of a range of delays,his invention uses fixed values for the delays. The delays in hisinvention are not programmable either by a user interface or by systemconditions such as the duration of the compressor activation.

U.S. Pat. No. 4,842,044 (Flanders et al., 1989) provides a heating andcooling control system that works by energizing a fan or other fluidcirculating device to circulate fluid and effect thermal transfer ofenergy from the fluid to the spaces being heated and by deenergizing thecirculating means at a selected time interval after deenergization ofthe heating and control system. The '044 patent also claims a heatingcontrol system comprising a switching means to effect energization ofthe fluid circulating means, a switching control means that isenergizable in response to operation of the control circuit, and anadditional circuit means that energizes the switching control means aselected time interval after deenergization of the heating system. '044patent is intended to increase the time the fan is turned on after aheating cycle to improve energy efficiency. Unfortunately, it drawspower continuously from the gas solenoid through a 680 ohm resistor, andthis method has proven to be problematic in practice. Too much currentdrawn in this way, can cause a humming noise in the gas valve and evenfalse operation. The patented device also enables the fan relay toactivate the blower as soon as the gas valve is activated. This resultsin cool air being circulated throughout the home since the plenum is notsufficiently warm. Normal heat operation retards the blower until thetemperature in the plenum reaches a preset operating temperature. The'044 patent also requires the addition of a relay circuit. This relaymust be active the entire time the fan is to be off, creating asignificant current draw even when the system is in not calling forheating or cooling. The '044 patent also describes fixed delays. It hasno way to adapt the fan delay times either by user input or by thecompressor run time. The delays provided by the '044 patent are alsosubject to the variations of the components selected. Additionally,although Flanders touches on the subject of how his invention works whenthe fan switch on the thermostat is moved from the AUTO position to theON position, as described, there is no way for the fan to come on whenthe homeowner requests.

In U.S. Pat. No. 4,136,703, Kinsey teaches of a device that interveneswith the controls coming from a thermostat and going to theheating/cooling system. His invention places a fixed upper limit to thetime that the compressor or heating source can be activated and then hisinvention adds additional time to the blower fan. This activity canincrease the efficiency of an air conditioner system by allowing acertain amount of water to condense on the evaporator coil and thenre-evaporating this water to cool the home. The amount of watercollected will vary based on the humidity of the ambient air. Having afixed compressor run time with a fixed blower time can create a lessefficient system than the current invention. In many environments,limiting the compressor run time and counting on evaporative cooling toreduce the home's temperature will increase the time required to coolthe home. In many cases, the desired set point may never be achieved.

In U.S. Pat. No. 7,240,851 Walsh teaches of a furnace fan timer. Hisdevice is strictly a timer with a user programmable interval andduration. His device runs continuously in a never ending loop countingdown minutes before operating the fan and then counting the minutes tokeep the fan activated. Walsh's device is not compatible with airconditioner systems. Most thermostats connect the fan switch to the airconditioner compressor switch when operating in the automatic fan mode.In systems with air conditioners, Walsh's invention will activate theair conditioner compressor when it turns on the fan. This requires usersto turn off the circuit breakers for their air conditioner systems whenusing his device. Walsh's invention has two interchangeable wireconnections. The present invention has at least three wires and eachconnects to a specific location on the thermostat.

The main objects of the present invention are:

(1) to provide a thermostat fan extended time delay device that does notrequire any special power connection; and

(2) to minimize any wiring modifications to accommodate the device; and

(3) to adapt the extended time delay based on the length the thermostatcalled for compressor or fan switch operation as well as user selectableparameters; and

(4) to adjust the extended time delay based on user selected parameters.

BRIEF SUMMARY OF THE INVENTION

The majority of this discussion deals with the most complicatedcontrolling mode of air conditioning. The present invention covers anexternal thermostat fan controller that comprises a microprocessor, anAC/DC converter, zero crossing detector, a switching device, and a userinterface, and that connects directly to an existing thermostat withminimal need for rewiring. The invention also encompasses a unique andnovel way of deriving power for the device's microprocessor that doesnot rely on an external power source. The controller of the presentinvention can operate with a minimum of three leads which can beconnected directly to the wiring presented to the standard householdthermostat, and a user can program the duration of the extended timedelay for the fan, or the device itself can determine the amount of theextended time delay for the fan based on the run time of the compressoror fan switch. In the preferred embodiment, all delay calculations areeither done autonomously using an algorithm based on compressor/fan runtime, or done with a single button.

The controller according to the present invention causes an extension inthe fan run time to increase the efficiency of air conditioning units inhot and dry climates. In most air conditioning systems, the fan isturned off simultaneously with the compressor. This wastes two kinds ofcooling still available. The mass of the cooling evaporator is stillvery cold then the compressor turns off. Running the fan after thecompressor stops allows this cooling to be captured and delivered intothe home. The second type of cooling available is using the moisturethat has condensed on the evaporator coils. By running the fan after thecompressor has stopped, the moisture is evaporated and the systemfunctions as an evaporative cooler, commonly known as a swamp cooler.This evaporation cooling is only applicable in hot and dry climates. Itwould not work as well in areas with high humidity. Studies have beendone showing a 10-17% rise in an air conditioning system EER using anextended time delay on the fan. Many new air conditioning systemsincorporate a fixed delay directly into their new products. The presentinvention allows this modern feature to be applied to the installed airconditioner base in hot and dry environments. The user interface can beany form that fits the function, including, but not limited to, an LCDdisplay and keypad, jumpers on the circuit board, or two LEDs and aswitch. The switching device can be any device that serves the requisitefunction; in the preferred embodiment, it is a triac. If the switchingmeans is an electro-mechanical switch, then the invention furthercomprises a battery to power the microprocessor when the switch isclosed.

When the thermostat is selected to heating mode, the controlleraccording to the present invention adds more time to the fan run time,either a fixed amount, or the amount the user programs via the userinterface.

The present invention includes a method of extending the cooling systemor heating system fan run time using the thermostat fan controller ofthe present invention.

In accordance with one aspect of the invention, a 60 Hz electricalsignal is employed as a time base and therefore has precise timing anddoes not vary from system to system or by aging or temperature of thecomponents.

In accordance with another aspect of the invention, a controllerselectively gates a triac for milliseconds and in doing so, has a totalcurrent draw on the order of 100 microamps. This is a current drawimprovement of 800% compared to known systems.

In accordance with still another aspect, the present invention controlsthe fan relay through the entire cycle without interruption, preventingrelay chatter and excessive wear.

In accordance with yet another aspect, the present invention restoresall connections to their original states when turned off providing anoverride function if the unit fails.

In accordance with another aspect, the current invention supports notonly a precisely fixed delay, but an adaptable delay based on compressor“on” time and it also supports a programmable delay where the user caninput the total number of minutes to delay.

In accordance with still another aspect, the present invention does notrequire the neutral leg of the AC transformer and can therefore beattached directly to the signals present at the thermostat. The presentinvention employs an innovative method of powering itself using the hotline and the control lines from the thermostat.

In accordance with yet another aspect, the present invention draws verylittle power when the heating/cooling system is not active since thereis no relay to be controlled.

In accordance with another aspect, the present invention worksregardless of the fan switch position in “ON” or “AUTO” position.

In accordance with yet another aspect, the present invention does notlimit the amount of time the compressor operates and thus maintainssystem efficiency. The present invention relies on the thermostat todetermine when the desired set point has been reached, and only thendoes it extend the fan run time. This ensures the homeowner's comfortand provides for the efficiency gains at the end of the cycle. Thepresent invention also can be mounted directly at the thermostat whereasknown systems require constant 24 VAC power for the use of switchingrelays.

In accordance with still another aspect, the present invention doesnothing until the thermostat calls for heating or cooling. Once thethermostat calls for cooling or heating, the present invention canextend the fan run time for either a fixed duration or an adaptableduration based on the time the compressor was active.

In accordance with yet another aspect, the present invention is designedspecifically to work with systems containing both heating and airconditioning. Known systems requires a user interface to enter theduration and interval. Once entered, the fan run time is not variable.The present invention may contain a user interface, but does not requireone. It measures the amount of time the compressor was active anddetermines the fan run time automatically. The present inventioninterrupts the signal from the thermostat to the fan relay and overridesthe fan control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial illustration of the preferred embodiment of thepresent invention.

FIG. 2 illustrates, in block diagram form, the configuration of thepresent invention in relation to an existing household thermostat.

FIG. 3 illustrates, in block diagram format, the components of thepresent invention.

FIG. 4 is a graph illustrating the timing associated with powering thepresent invention.

FIGS. 5 and 6 illustrate, in block diagram form, the programming of thepreferred embodiment of the present invention.

REFERENCE NUMBERS

-   -   201 Existing household thermostat    -   202 Furnace/heat producing control circuitry    -   203 Air conditioning compressor control    -   204 Fan contact terminal    -   205 Fan/blower relay    -   206 System fan/blower    -   207 Air conditioning contact terminal    -   208 Heater contact terminal    -   209 Hot contact terminal    -   210 System 24 VAC transformer    -   211 External thermostat fan controller    -   212 Fan relay lead    -   213 Transformer Hot lead    -   214 Thermostat fan activation switch lead    -   215N/AOptional lead to thermostat A/C compressor terminal 207.    -   216 Optional lead to thermostat heat terminal    -   217 Break in wiring from thermostat to fan relay    -   301 Switching device    -   302 Zero crossing detector    -   303 AC/DC converter    -   304 Microprocessor    -   305 User interface    -   306 Optional battery    -   307A On/Off Switch in “ON” position    -   307B On/Off Switch in “OFF” position    -   500-520 Flow diagram blocks    -   601-613 Flow diagram blocks

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a pictorial illustration of a fan controller 211 according tothe present invention. The fan controller 211 can connect directly to anexisting thermostat through the use of only three wires. It can bemounted on the wall near the thermostat or located anywhere else in thehouse, as long as it can be connected to the thermostat wires.

FIG. 2 illustrates, in block diagram form, the configuration of thepresent invention in relation to an existing household thermostat 201.The thermostat 201 is typically connected as shown when the home has afurnace/heat producing control circuitry 202 and air conditioningcompressor control 203. Prior to the installation of the presentinvention, the fan contact terminal 204 connects the thermostat 201 tothe fan/blower relay 205. With the addition of the fan controller 211,this connection is interrupted as shown by dashed line 217 and theterminal 204 is connected to terminal 214 of the fan controller 211 andterminal 212 of the fan controller 211 is connected to the fan relay205. When actuated, the fan relay 205 connects the system fan/blower 206to the 120 VAC. The air conditioning (A/C) contact terminal (A/C Y) 207connects the thermostat 201 to the air conditioning compressor control203. 215 and 216 show a connection from the thermostat terminal blocks207 and 208. The heater contact terminal 208 connects the thermostat 201to the heat producing control circuitry 202. The hot terminal 209connects the thermostat 201 to the hot side of the 24 volt ACtransformer 210.

Optional lead 216 shows a connection from the heater contact terminal208 of the thermostat 201 to the fan controller 211. This wiring path isoptional when the fan controller 211 is used in a system where the heatfan time is extended. In the preferred embodiment no additional powerconnections are required, unlike some prior art, which requires either adedicated connection to the transformer or another relay. The fancontroller 211 draws power through the fan/blower relay 205. This lackof external power is new and innovative as compared to prior art.

FIG. 3 illustrates, in block diagram format, the components of the fancontroller 211. A microprocessor 304 is used to control a switchingdevice 301, receive input and provide output to a user interface 305.The microprocessor 304 receives power from an AC/DC converter 303 andalso receives input from a zero crossing detector 302, the line from atransformer hot lead terminal 213 electrically connected to the hotcontact terminal 209 of the transformer 201, and optionally the inputthat enables the NC compressor. The microprocessor 304 performs severalmajor functions. In terms of timing, the microprocessor 304 keeps trackof seconds and minutes by monitoring the AC line signal. Each positivezero crossing accounts for 1/60_(th) of a second; therefore, sixtypositive crossings occur each second. The seconds are then accumulatedto keep track of minutes. The negative crossings are also monitored toprovide timing for a switching device 301. The switching device 301could be either a standard relay type device, a reed relay or some otherelectromechanical device. It could also be a solid state device such asan FET switch or a triac. Each switching device requires minormodifications to the baseline design, but each manifestation of theswitching device is covered by the present invention. The description ofthe preferred embodiment is based on a triac switch, but the presentinvention is not limited by the type of switching device. In the eventthe switching device 301 is a triac, it must be triggered at eachpositive and negative zero crossing of the AC line.

The user interface 305 comprises an input device to the microprocessor304 and visual outputs to the user that enable the programming of thefan delay timing and methods. The microprocessor 304 continuouslymonitors the user interface 305 to determine if there is any change tothe current system operation. If a change is requested by the user, thecurrent programming of the switch state is set to neutral (the switchingdevice 301 is turned off) and the user interface 305 is monitored todetermine the user's requested action. In the preferred embodiment, themicroprocessor contains an EEPROM, which allows the unit to store theuser's programming instructions when there is no power applied to theunit.

The AC/DC converter 303 is used to condition the input 24 VAC signalinto a DC signal necessary to operate the DC devices within the unit.The zero crossing detector 302 is used to condition the AC input to alevel that will not damage the microprocessor 304. The microprocessor304 generates an interrupt in both the positive going and negative goingzero crossings and uses this zero crossing timing to keep track ofelapsed time and also to determine when to fire the triac, which may beused as the switching device 301. While the description of the preferredembodiment is based on a triac switch, the present invention is notlimited by the type of switching device and the switching device 301 maybe a standard relay, a reed relay or some other electro-mechanicaldevice, or a solid state device such as an FET switch.

There are four operating modes, each with different user interfaces,that are manifested in the single product and circuit board. The first,mode 1, is a fixed fan timing extension. It could be anywhere from 2minutes to mode than 10 minutes, but whatever it is, it is fixed andconstant. Mode 1 requires no special user interface, neither buttons norLED indicators. The timing delay can be set using jumpers or switchesmanufactured into the circuit board.

The second mode, mode 2, is an adaptive mode. The processor 304 monitorsthe duration the fan or compressor is activated by the thermostat 201,and it adjusts the delay accordingly. If the compressor is run for ashort period of time and there is not much condensation on theevaporator, the fan time will be extended for a shorter period of time.Likewise, if the compressor has run for a longer period of time,allowing for more condensate, the fan will run for a longer period oftime after the compressor has stopped. There is nothing to preclude theadjustment of the algorithm to support a variety of operatingparameters. If it turns out in the future that the timing table needs tobe reversed, that would be an obvious extension of the capabilities ofthe present invention. Mode 2 requires no special user interface,neither buttons nor LED indicators.

Mode 3, is a programmable mode. In the preferred embodiment, the userinterface 305 would be compromised of a single switch and a single LED.The user simply inputs the number of minutes to run the fan after thecompressor stops by tapping the button while the fan controller 211 islistening for input. This user interface is not intended to preclude theuse of switches or other ways of programming the fan time extension.

Mode 4, is a combination of mode 2 and mode 3. Mode 4 allows the user toselect whether to operate in adaptive mode as in mode 2 or the user mayinput a number of minutes to run the fan. When mode 4 is set to theadaptive method, the user can input additional parameters to theadaptive algorithm so fine tuning can occur. These additional parametersare input using the same single push button but a different color of LEDindicator. This could be a completely different LED or a single LEDcapable of multiple colors. FIG. 6 is a detailed flow chart of theinteraction between the LEDs and the switch when operating in mode 4.

The preferred embodiment of the present invention using a triac does notrequire a battery. The fan controller 211 draws its power through the 24VAC transformer 210 (see FIG. 2 ). In the event that anelectro-mechanical switch was used, either an optional battery would beadded to power the microprocessor 304 or the additional lines 215 and216 could provide power when the switch is closed.

FIG. 4 shows graphs that illustrate the timing associated with poweringthe present invention. Because power is drawn through the fan/blowerrelay 205 (see FIG. 2 ), when the fan/blower relay is not actuated, 24VAC is applied to the terminals of the fan controller 211. That power issufficient to drive the fan controller 211 and all its components.Normally, to actuate the fan relay, the fan switch must appear closed,in other words, in FIG. 2 , the fan contact terminal 204 must be shortedto the hot contact terminal 209. This situation creates a problem foranything that is trying to draw power from these terminals because theyare now shorted and there is no power available.

The present invention uses an innovative way to draw power. In thepreferred embodiment of the invention, using a triac as the switchingdevice 301, the microprocessor does not enable the triac at exactly thezero crossing of the 24 VAC signal. Instead, it delays an amount of timeinto the positive going cycle and allows the positive going waveform toprovide a small amount of charge into the AC/DC circuitry. This chargeis represented by the dark areas in FIG. 4A. After a small charge hasbeen accumulated, the microprocessor 304 enables the triac to pass theremainder of the power through to the fan relay 205. This occurrence isrepresented by FIG. 4B. These figures show the AC waveform rising for ashort period and then completely shorted out for the duration of thecycle, which passes this energy on to the fan relay 205 and thusactuates it. In this way, the fan relay 205 gets the majority of the ACwaveform and actuates, while enough charge is stored by the AC/DCcircuitry to keep the microprocessor 304 running until the next positivegoing cycle of the AC waveform.

In another embodiment of the present invention, a battery 306 could beused to supply power to the microprocessor 304 when the fan controller211 is actuating the fan/blower relay 205. In this situation, the 24 VACsignal would be passed to the fan/blower relay 205. This method is lesscomplex but increases the cost of the invention and adds an item (thebattery) that requires maintenance and periodic replacement.

FIG. 5 illustrates, in block diagram format, the programming of thepreferred embodiment of the present invention. The programming is formode 4 of the invention, the most complicated. All other modes are asubset of mode 4 and can be easily achieved by eliminating steps. Theroutine begins at a hardware reset and then proceeds to the first block500. The interrupt routine begins at block 515. Block 500 indicates thatwhen power is first applied to the present invention, the last storedoperating mode and minutes to delay are retrieved from the non-volatilestorage, and the present invention is initialized to the last programmedstate. Block 501 indicates that the invention will blink the LEDs tovisually indicate the last programmed state. If the device was last in auser selected delay mode, the green LED will blink to indicate thenumber of minutes the user last entered as a delay. If the device waslast in an adaptive mode, the unit will blink the red LED to reflect theparameters entered into the adaptive algorithm.

Decision block 502 is used to determine if the user would like to enterdevice information, or just go to the main loop. If decision block 502determines that there is a button pressed, then the routine proceeds toblock 503 and immediately clears the fan on flag, which causes the fanto be turned off at the next interrupt. The present invention thendelays for three seconds as indicated in block 504. The button is againtested as shown in decision block 505. If the button was released beforethe three seconds are up, then the programming loop is aborted, and theunit restarts at block 501.

If the button was held down for at least three seconds as indicated indecision block 505, it is clear that the user wishes to change theprogramming. The green “Duration” LED is illuminated shown in block 506,which indicates to the user that the invention is ready to accept buttontaps as programming input for the run time delay. Once the green“Duration” LED is illuminated, the unit begins another three-secondinternal controller. If the user releases the button within threeseconds of seeing the green LED illuminated, as determined in decisionblock 507, then the routine enters the “Duration” programming mode asshown in blocks 512 through 514.

Block 512 indicates that the user now taps the programming button from 0to 96 times, which internally is interpreted as the number of one minuteperiods that the present invention will elongate the fan operation. Inother words, if the user taps the button four times, the presentinvention will keep the fan active for four minutes after the compressorhas stopped. Block 514 indicates that after the user has tapped in thenumber of one minute periods of fan time extension and released thebutton for three seconds, the invention stores the new program into thenon-volatile storage as indicated in block 514 and then restarts fromthe beginning at block 501. If the user enters the programming mode andat any step does not enter any button taps, the present invention willrevert to the last number of taps that was stored in the non-volatilememory for the duration.

In addition to the function described above, block 507 also determinesif the button was not released within three seconds of when the green“Duration” LED was illuminated. Continuing to depress the programmingbutton after the green “Duration” LED was illuminated indicates to thepresent invention that the user wishes to skip the duration programmingand proceed to program the adaptive algorithm parameters. The presentinvention indicates that it is ready to accept adaptive algorithmparameters by extinguishing the green “Duration” LED and illuminatingthe red “Adaptive” LED. This is indicated in block 508 and is the signalto the user that adaptive algorithm parameters are ready to beprogrammed. This programmability allows multiple inputs to the adaptivealgorithm such as a multiplier to the baseline adaptive delay.

At decision block 509, the present invention waits for the user torelease the programming button. Block 510 is used to count the number oftaps the user enters for the adaptive algorithm parameters. Forinstance, there can be four pre-set adaptive algorithm parameters, andthe user taps the button once, twice, three or four times to indicatewhich setting would be optimal for the current cooling configuration.Block 511 stores the new adaptive algorithm parameters into thenon-volatile memory, and the unit restarts from the start at block 501.

Block 515 indicates the beginning of an interrupt routine. This routineis entered at the rising and falling zero crossings of the 24 VACsignal. The interrupt routine first determines if the fan is scheduledto be on in decision block 516. If not, the routine merely updatesinternal controllers 519 by counting the number of 60 Hz transitions onthe 24 VAC power input line.

After delaying the amount of time into the interrupt cycle based onrising or falling edge as shown in block 517, block 518 fires the triac,and the remainder of the 24 VAC signal is passed on to the fan relay,thus energizing the relay for this 60 Hz cycle. The interrupt routinethen follows the actions as described above by updating the internalcontrollers, block 519. Block 520 returns from the interrupt to thecalling routine.

FIG. 6 illustrates the main loop of the preferred embodiment. Block 601is the start of the main loop. Block 602 is used to determine if the fanor compressor is activated by the thermostat. If neither are activated,the routine uses block 610 to determine if it is time to blink eitherthe red or green led to indicate the unit is on and in a healthy stateas shown in block 611. The unit then looks to see if the button waspressed. If so, it is an indication that the user would like to changesome of the parameters and the unit restarts itself and prepares toinput button presses. If block 602 determines that the thermostat iscalling for the fan to be activated, block 603 sets the “fan on” flag.This flag is a indicator to the interrupt routine that the switchingdevice 301 should be activated on the next rising edge of the 60 Hzsignal. The routine then accumulates the total time the thermostat iscalling for the fan to be active as shown in block 604. This isaccumulated value is input to the adaptive algorithm to automaticallydetermine the extended fan run time based on the time the thermostatcalled for the fan to be on.

Decision block 605 simply looks to see it the thermostat is calling forthe fan to be activated, either through the fan switch, or the optionalconnection to the thermostat cooling contact 207. If the fan is stillactive, simply accumulate more time. Decision block 606 determines ifthe invention is in adaptive mode or programmable mode. If inprogrammable mode, block 612 looks up the number of minutes the userentered and drops into a loop to keep the fan on for that number ofminutes. If the invention is in adaptive mode, the total time the fanwas activated by the thermostat and the user input parameters areentered into an algorithm to determine the duration to keep the fan on.A simple algorithm, block 607, could take the form of a look up table asshown in Table 1 below:

TABLE 1 Fan run time extension based on user selectable parameters UserUser User User Thermostat parameter parameter parameter parameter Fan ontime 1 2 3 4 0-5 min 1.5 2 2.5 3 5-10 min 3 4 5 6 10-15 min 4.5 6 7.5 915 min+ 6 8 10 12

Although the preferred embodiment of the present invention has beenshown and described, it will be apparent to those skilled in the artthat many changes and modifications may be made without departing fromthe invention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

DEFINITIONS

The term “AC/DC” means Alternating Current/Direct Current.

The term “FET” means Field-Effect Transistor.

The term “Hz” means “hertz” or a unit of frequency equal to one cycleper second.

The term “LCD” means Liquid Crystal Display.

The term “LED” means Light Emitting Diode.

The term “triac” means a three-terminal semiconductor for controllingcurrent in either direction.

The term “VAC” means Volts, Alternating Current.

I claim:
 1. A method for connecting an external fan controller (211) toan existing Air Conditioning (AC) system including a system fan (206),and controlling the fan by the external fan controller, the methodcomprising: positioning the external fan controller; disconnecting a fanrelay lead (217) originally connecting a thermostat fan “G” terminal(204) to a fan relay (205) controlling the fan, from the thermostat fan“G” terminal (204); reconnecting the fan relay lead to a fan activationswitch output terminal (212) of the external fan controller; connectingthe thermostat fan “G” terminal to a fan terminal input (214) on theexternal fan controller; connecting an A/C compressor terminal (207) ofthe thermostat to an AC compressor input (215) of the external fancontroller (211); leaving an original AC compressor lead in placebetween an AC compressor terminal of the thermostat and an ACcompressor; and leaving a power signal lead in place between atransformer and the thermostat; connecting a power signal lead from asystem transformer (210) to a low-voltage input (213) of the fancontroller (211); and the external fan controller controlling a run timeof the fan, comprising the steps of: monitoring a duration of each ACcompressor cycle; determining a variable amount of time a fan operationis extended after each cooling cycle based on the duration of each ACcompressor cycle; and extending the fan operation after the end of eachcooling cycle for the variable amount of time based on the duration ofeach AC compressor cycle.
 2. The method of claim 1, wherein the externalfan controller does not include a user interface.
 3. The method of claim1, further including a step of connecting a sole power signal for theexternal fan controller in parallel with a hot contact terminal of thethermostat.
 4. The method of claim 1, further including the external fancontroller extending a run time of the fan for a factory programmablefixed duration after an end of a cooling cycle.
 5. The method of claim1, wherein the controller extends the fan run time for a userprogrammable fixed amount after a cooling cycle.
 6. A method forconnecting an external fan controller to an existing Air Conditioning(AC) system including a fan, and controlling the fan by the external fancontroller, the method comprising: positioning the external fancontroller; disconnecting a fan relay lead originally connecting athermostat fan terminal to a fan relay controlling the fan, from thethermostat fan terminal; reconnecting the fan relay lead to a fanactivation switch terminal of the external fan controller; connectingthe thermostat fan terminal to a fan terminal on the external fancontroller; leaving an original AC compressor lead in place between anAC compressor terminal of the thermostat and an AC compressor;connecting an A/C compressor terminal of the thermostat to an ACcompressor input of the external fan controller; leaving a power signallead in place between a transformer and the thermostat; and the externalfan controller controlling a fan run time of the fan, comprising thesteps of: monitoring a duration of each AC compressor cycle; anddetermining a variable amount of time a fan operation is extended aftereach cooling cycle based on each duration.
 7. The method of claim 1,further including: monitoring the duration of the air conditionercompressor cycle; and determining an amount of time the fan operationextension based on user selected values after the cooling cycle.
 8. Themethod of claim 1, wherein the external fan controller includes a userinterface comprising an LCD display and keypad.
 9. The method of claim1, wherein the external fan controller includes a user interfacecomprising at least one LED and one switch.
 10. The method of claim 1,further including programming the external fan controller using a singlebutton.
 11. The method of claim 1, further including the external fancontroller determining whether it is operating in fixed delay mode oradaptable delay mode, wherein both the fixed and adaptable mode can beprogrammed with a single button.
 12. The method of claim 1, wherein theexternal fan controller includes a triac, and including a step ofswitching the fan relay on and off by the triac.
 13. The method of claim1, wherein the external fan controller includes an electro-mechanicalswitch, a microprocessor controlling the external fan controller, and abattery to power the microprocessor when the electro-mechanical switchis closed, and including a step of switching the fan relay on and off bythe electro-mechanical switch.
 14. A method for connecting an externalfan controller to an existing Air Conditioning (AC) system including afan, and controlling the fan by the external fan controller, the methodcomprising: positioning the external fan controller; disconnecting a fanrelay lead originally connecting a thermostat fan terminal to a fanrelay controlling a fan, from the fan relay; reconnecting the fan relaylead to a thermostat fan activation switch terminal of the external fancontroller; connecting a second fan relay lead from a fan relay terminalon the external fan controller to the fan relay; leaving an original ACcompressor lead in place between an AC compressor terminal of thethermostat and an AC compressor; connecting an A/C compressor terminalof the thermostat to an AC compressor input of the external fancontroller; leaving a power signal lead in place between a transformerand the thermostat; and wherein the external fan controller performs thefollowing actions: monitoring a duration of each AC compressor cycle;determining a variable amount of time a fan operation is extended aftereach cooling cycle based on the duration of each AC compressor cycle;and the external fan controller controlling a fan run time of the fanfor the variable amount of time for each AC compressor cycle.
 15. Amethod for connecting an external fan controller to an existing AirConditioning (AC) system including a fan, and controlling the fan by theexternal fan controller, the method comprising: positioning the externalfan controller; disconnecting a fan relay lead originally connecting athermostat fan terminal to a fan relay controlling a fan, from the fanrelay; reconnecting the fan relay lead to a thermostat fan activationswitch input terminal of the external fan controller; connecting asecond fan relay lead from a fan relay output terminal on the externalfan controller to the fan relay; leaving an original AC compressor leadin place between an AC compressor terminal of the thermostat and an ACcompressor; connecting an A/C compressor terminal of the thermostat toan AC compressor input of the external fan controller; leaving a powersignal lead in place between a system transformer and the thermostat;connecting a sole power signal for the external fan controller inparallel with the power signal lead of the thermostat; and the externalfan controller controlling a fan run time of the fan, comprising thesteps of: monitoring a duration of each AC compressor run time;determining a variable amount of time a fan operation is extended aftereach AC compressor AC compressor run time based on the duration of eachAC compressor run time.
 16. The method of claim 1, wherein duration ofthe AC compressor cycle is at least one duration selected from the groupconsisting of: an AC on time, and an AC off time.
 17. The method ofclaim 6, wherein duration of each AC compressor cycle is at least oneduration selected from the group consisting of: an AC compressor ontime, and an AC compressor off time.
 18. The method of claim 14, whereinduration of each air conditioner compressor cycle is at least oneduration selected from the group consisting of: an AC on time, and an ACoff time.
 19. The method of claim 1, wherein duration of each ACcompressor cycle is an AC compressor on time.
 20. The method of claim 6,wherein duration of each AC compressor cycle is an AC compressor ontime.
 21. The method of claim 14, wherein duration of each AC compressorcycle is an AC compressor on time.
 22. The method of claim 1, whereinmonitoring the duration of each AC compressor cycle is based on whetheror not the fan or AC compressor are activated by the thermostat based onthe presence or absence of at least one signal selected from the groupconsisting of: a fan signal, and an AC compressor signal.
 23. The methodof claim 6, wherein monitoring the duration of each AC compressor cycleis based on whether or not the fan or AC compressor are activated by thethermostat based on the presence or absence of at least one signalselected from the group consisting of: a fan signal, and an ACcompressor signal.
 24. The method of claim 14, wherein monitoring theduration of each AC compressor cycle is based on whether or not the fanor AC compressor are activated by the thermostat based on the presenceor absence of at least one signal selected from the group consisting of:a fan signal, and an AC compressor signal.
 25. The method of claim 1,wherein monitoring the duration of each AC compressor cycle is based onwhether or not the fan or AC compressor are activated by the thermostatbased on the presence or absence of a thermostat call for cooling. 26.The method of claim 6, wherein monitoring the duration of each ACcompressor cycle is based on whether or not the fan or AC compressor areactivated by the thermostat based on the presence or absence of athermostat call for cooling.
 27. The method of claim 14, whereinmonitoring the duration of each AC compressor cycle is based on whetheror not the fan or AC compressor are activated by the thermostat based onthe presence or absence of a thermostat call for cooling.